1. Technical Field
The present invention relates to a method for reusing a secondary battery, and more particularly to a method for combining secondary batteries reclaimed from users to reconstruct a newly assembled battery or battery pack.
2. Related Art
Assembled batteries each composed of a plurality of secondary batteries are used as power sources for electric vehicles, hybrid electric vehicles, or the like. On the other hand, from the viewpoint of efficient utilization of resources, in connection with assembled batteries used as a power source for vehicles, reusing techniques or reconstructing (rebuilding) an assembled battery having performance sufficient for reuse from assembled batteries reclaimed from users to enable resupply of a battery to a user have also been considered. With respect to rebuilding, because battery characteristics, such as variations in voltage due to overcharge, overdischarge, or memory effect, vary among assembled batteries which have been used, there has been proposed a structure wherein secondary batteries which have particularly superior battery performance are selected for rebuilding from among a plurality of reclaimed secondary batteries.
Japanese Patent Publication No. JP 2003-17142 A discloses a method for reusing a battery pack which houses a battery module in which a plurality of unit cells that are sealed-type nickel-metal hydride batteries are combined, the method comprising reclaiming a battery pack as a battery to be replaced when it is determined that the battery pack has reached its end of life, renewing unit cells or battery modules for which an end-of-life determination has been made by refilling them with an electrolytic solution, and reassembling them into a battery pack. An end-of-life determination is made when an internal resistance calculated for each unit cell or each battery module becomes greater than a specified value, or based on whether or not a variation in remaining capacity or voltage between unit cells or between battery modules becomes greater than a specified value.
Further, Japanese Patent Publication No. JP 2007-141464 A discloses a method for reusing a secondary battery module of a secondary battery system which includes one or more secondary battery modules, the method comprising the steps of obtaining, from the secondary battery system, at least one or more pieces of battery information selected from a resistance, a capacity, a battery use time, a resistance change rate, a capacity change rate, and a battery use intensity of a secondary battery module constituting the secondary battery; determining whether or not an obtained piece of battery information has reached a threshold value which is preset for that piece of battery information; reclaiming the secondary battery module when it is determined that the threshold value has been reached; grading the reclaimed secondary battery module in accordance with performance of the battery determined based on the battery information of the reclaimed secondary battery module; and, based on a result of the grading, applying the reclaimed secondary battery module to a system having threshold value conditions under which it can operate at the performance of the battery that the secondary battery module has at the time when it is being reclaimed.
Further, Japanese Patent Publication No. JP 2009-277627 A discloses carrying out reconstruction to create a newly assembled battery by combining reusable secondary batteries of an originally recycled battery or another battery that is stored in a fully discharged state, or by combining the secondary battery to be reused and a new secondary battery.
In cases where a newly assembled battery (or battery pack) or secondary battery system is reconstructed (rebuilt) by comparing an internal resistance or a capacity of unit cells or battery modules with a preset threshold value to determine whether or not an end of life has been reached, reclaiming the unit cells or battery modules, and grading them, although the internal resistance or the capacity value of the unit cells or battery modules constituting the rebuilt battery pack satisfies a reference value when it is rebuilt, there are relatively large overall variations when it is rebuilt, and the variations may further increase as the rebuilt assembled battery is used. For example, assume a case where there are two assembled batteries A and B for which it is determined that an end of life has been reached, and battery modules are taken from these two assembled batteries to rebuild a new assembled battery C. When the new assembled battery C is rebuilt by respectively grading a plurality of battery modules constituting the assembled battery A, respectively grading a plurality of battery modules constituting the assembled battery B, and putting together battery modules having a predetermined grade from the assembled battery A and battery modules having the same grade from the assembled battery B, because there are variations in, for example, internal resistance or voltage even among those having the predetermined grade of the assembled battery A, and there are variations in, for example, internal resistance or voltage even among those having the same grade of the assembled battery B, a range of variations in battery characteristics of the battery modules of the newly rebuilt assembled battery C is relatively large. When attention is focused on the assembled battery A, although, even if there is no problem in battery characteristics themselves such as internal resistance or voltage, it is more preferable not to incorporate battery modules having battery characteristics significantly deviated from battery characteristics of other battery modules included in the assembled battery A into the assembled battery C which is to be newly rebuilt, in conventional methods, such battery modules will be incorporated because there is no problem in battery characteristics themselves. This similarly applies to the assembled battery B.